A Bright and Ionizable Cytosine Mimic for i‑Motif Structures

A new fluorescent cytosine analog “tsC” containing a trans-stilbene moiety was synthesized and incorporated into hemiprotonated base pairs that comprise i-motif structures. Unlike previously reported fluorescent base analogs, tsC mimics the acid–base properties of cytosine (pK a ≈ 4.3) while exhibit...

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Bibliographic Details
Published in:Bioconjugate chemistry 2023-06, Vol.34 (6), p.972-976
Main Authors: Karimi, Ashkan, Wang, Kaixiang, Basran, Kaleena, Copp, William, Luedtke, Nathan W.
Format: Article
Language:English
Subjects:
Base Pairing
Base pairs
Base Sequence
Circular Dichroism
Cytosine
Cytosine - chemistry
Dichroism
Emission analysis
Fluorescence
Humans
Hydrogen-Ion Concentration
Nucleic Acid Conformation
Protonation
Single-stranded DNA
Stilbene
Wavelengths
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Summary:A new fluorescent cytosine analog “tsC” containing a trans-stilbene moiety was synthesized and incorporated into hemiprotonated base pairs that comprise i-motif structures. Unlike previously reported fluorescent base analogs, tsC mimics the acid–base properties of cytosine (pK a ≈ 4.3) while exhibiting bright (ε × Φ ≈ 1000 cm–1 M–1) and red-shifted fluorescence (λem = 440 → 490 nm) upon its protonation in the water-excluded interface of tsC+:C base pairs. Ratiometric analyses of tsC emission wavelengths facilitate real-time tracking of reversible conversions between single-stranded, double-stranded, and i-motif structures derived from the human telomeric repeat sequence. Comparisons between local changes in tsC protonation with global structure changes according to circular dichroism suggest partial formation of hemiprotonated base pairs in the absence of global i-motif structures at pH = 6.0. In addition to providing a highly fluorescent and ionizable cytosine analog, these results suggest that hemiprotonated C+:C base pairs can form in partially folded single-stranded DNA in the absence of global i-motif structures.
ISSN:1043-1802
1520-4812
DOI:10.1021/acs.bioconjchem.3c00055